Investigating amino acid metabolism and accumulation in Sauvignon blanc grapes in response to canopy manipulation

Abstract

Vitis vinifera var. Sauvignon blanc is the major commercial grape variety grown in New Zealand. Emphasising the importance of this single variety, it represented 66% of the entire grape production in 2013 and 84% of New Zealand's wine exports. Amino acids (AAs) are important compounds that occupy a pivotal position in grapevine metabolism and play a major role in the biological functions of fermentative microbes. Nitrogen status and AAs influence not only general vine homeostasis, but biochemical composition of the grape berry, which can be hugely varied. In turn, the biochemical composition of the berry is the major determinant of wine quality through yeast growth, fermentation kinetics and flavour/aroma metabolism. We have previously investigated changes in Sauvignon blanc grape AA composition. Removing leaves from around the fruiting zone significantly reduces total AAs in the berries/juice/must at harvest. Two AAs in particular, arginine and proline, accumulate to high levels and make up the highest proportion of total AA concentrations in the grape at harvest, with their substantial accumulation post­veraison being poorly understood. Both of these Ms are significantly decreased in experiments with our leaf removal treatments. To advance our understanding of the mechanisms involved in AA accumulation in Sauvignon blanc grapes, we have performed leaf removal experiments and quantified total Ms throughout development to define developmental stages where there is a "switch" in berries to assimilate (i.e. through glutamate and glutamine), accumulate, degrade or redistribute AAs. We have also investigated genetic regulation of nitrogen assimilation and amino acid metabolism. Using Nanostring nCounter technology has enabled us to simultaneously investigate multiple known and putative genes involved in AA assimilation (glutamine and glutamate) and proline/arginine metabolism. We will be presenting our initial results from these experiments and aim to provide insight to these findings.